According to at least one embodiment of the present disclosure, a well bore cementing system may comprise a spacer fluid and a cement slurry. The spacer fluid may be positioned within a well bore, and the spacer fluid may comprise a first surfactant package comprising one or more surfactants. The cement slurry may be positioned within the well bore, and the cement slurry may comprise a second surfactant package comprising one or more surfactants.

Methods and systems for the treatment of wells are disclosed. A method for treating a well comprises providing a treatment fluid comprising calcium-aluminate cement, water, and a cement set retarder; and introducing the treatment fluid into a wellbore. A system for treating a well comprises a treatment fluid comprising calcium-aluminate cement, water, and a cement set retarder; a vessel to contain the treatment fluid; a pumping system coupled to the vessel to pump the treatment fluid; and a conduit coupled to the pumping system.

In one embodiment, a retarded acid system comprises an aqueous acid and a retarding surfactant. The aqueous acid may comprise from 5 wt. % to 25 wt. % of a strong acid, that is, an acid having a K.sub.a greater than or equal to 0.01. The aqueous acid may further comprise from 75 wt. % to 95 wt. % water. The retarding surfactant may have the general chemical formula R(OC.sub.2H.sub.4).sub.XOH where R is a hydrocarbon having from 11 to 15 carbon atoms and x is an integer from 6 to 10. The retarding surfactant may have a hydrophilic-lipophilic balance from 8 to 16.

A method of treating a well comprising introducing a well treatment fluid into the well, and a well treatment fluid, are provided. The well treatment fluid comprises an aqueous base fluid, sepiolite clay, and a polymer component selected from the group of an acryloylmorpholine polymer, a polyvinylpyrrolidone polymer, and mixtures thereof. In one embodiment, for example, the method is a method of drilling a well. In this embodiment, the well treatment fluid is a drilling fluid.

A method of cementing a wellbore includes injecting into the wellbore a non-aqueous fluid; injecting into the wellbore a cement slurry and a non-ionic surfactant composition after injecting the non-aqueous fluid; and allowing the cement slurry to set, wherein the non-ionic surfactant composition comprises an alkyl end-capped ethoxylated fatty alcohol, a chain extended non-ionic surfactant, or a combination comprising at least one of the foregoing.

Spacer fluid compositions comprising water, a clay, and a sulfur-containing polyether surfactant are disclosed, and such compositions often can further include a weighting additive, an antifoaming additive, and a co-solvent. These spacer fluid compositions can be used to treat metal casing and to remove drilling fluid residue for improved cement bonding in wellbore applications.

Methods and systems for predicting properties of well bore treatment fluids are disclosed. An embodiment includes a method of predicting fluid properties comprising: determining an operational window for a well bore fluid system; collecting data at vertices of the operational window; and developing a model comprising predicted properties for a plurality of data points within the operational window, wherein developing the model uses Barycentric interpolation.

Embodiments of methods for reducing lost circulation in a wellbore comprise inserting a conduit comprising a first and second end and an outer diameter and an inner diameter into the wellbore, and pumping a thixotropic cement slurry, wherein the thixotropic cement slurry will increase in viscosity with no shear and decrease in viscosity with shear, and have a power law exponent value of less than or equal to 0.3 when the thixotropic cement slurry has a density of greater than 12.69 pounds per gallon, through the conduit into the wellbore, in which the thixotropic cement slurry comprises at least one cement, at least one viscosifier, mix water, and one or more than one strength accelerating additives. The method further comprises allowing the thixotropic cement slurry to harden in the wellbore to create a plug, removing the conduit from the wellbore, and reducing lost circulation via the plug in the wellbore.

In one embodiment, a retarded acid system comprises an aqueous acid and a retarding surfactant. The aqueous acid may comprise from 5 wt. % to 25 wt. % of a strong acid, that is, an acid having a K.sub.a greater than or equal to 0.01. The aqueous acid may further comprise from 75 wt. % to 95 wt. % water. The retarding surfactant may have the general chemical formula R(OC.sub.2H.sub.4).sub.XOH where R is a hydrocarbon having from 11 to 15 carbon atoms and x is an integer from 6 to 10. The retarding surfactant may have a hydrophilic-lipophilic balance from 8 to 16.

A spacer fluid contains one or more hydratable polymeric viscosifying agents having a particle size distribution such that a minimum of 90% of the particulates are retained on a 20 mesh screen. The spacer fluid may further contain one or more surfactants, viscosity thinners, organic solvents, weighting materials, suspending agents and antifoaming agents. The spacer fluid may be used to position a first fluid into a wellbore annulus of a wellbore containing a second fluid. The spacer fluid may further be used to fluidly isolate at least a portion of a wellbore annulus in a wellbore containing an oil-based drilling mud and an aqueous cement slurry.